The broad objectives of this research project are as follows: (a) To pursue our ongoing investigation on elucidating the amino acid sequence of certain peptides derived from the digestion of phosphofructokinase, e.g., (1) The acetylcarrying peptide (probably it is the N-terminal one); (2) The peptide carrying the post-translational phosphoryl group; (3) A peptide at the fructose 6-phosphate site which is to be labeled by an active site oriented analogue; and (4) The peptides resulting from treating rabbit muscle phosphofructokinase with cyanogen gromide. Our long-range goal is to determine the complete primary structure of phosphofructokinase and correlate its structure with its mechanism of action and regulation. (b) To carry out a comparative study of the activity, allorteric characteristics, and possible post-translational modification of the enzyme phosphofructokinase in muscle and liver of normal and diabetic rats in an effort to gain insight into the factors involved in the diminished activity of this key regulatory enzyme in the diabetic state. Several workers reported a block at the glycolytic step catalyzed by phosphofructokinase. However, no agreement has been established concerning its causation.